Engineering Papers⌕ Search

Engineering topics

Wang, H.

Publications and source records attributed to Wang, H..

At least 163 records · Page 9

A Monolithic W-Band Three-Stage LNA Using 0.1 Micron InAlAs/InGaAs/InP HEMT Technology

A monolithic W-band three-stage Low Noise Amplifiers (LNA) based on 0.1 um pseudomorphic InAlAs/InGaAs/InP (High Electron Mobility Transistors (HEMTs) has been developed. this LNA demonstrated a noise figure of 4.3 dB and an associated small signal gain of 19 dB at 100 GHz with a low dc power consumption of 20 mW. This is the best reported monolithic W-band LNA performance using InP-based HEMT technology and demonstrates the potential of InP HEMT technology for higher millimeter-wave applications.

Wang, H.↗

Boundary formulations for three-dimensional continuum structural shape sensitivity analysis

The direct, singular, boundary element analysis formulation is shown to provide a basis for a computationally efficient and accurate shape design sensitivity analysis approach for the structural response of three-dimensional solid objects. The theoretical formulation for surface displacement and traction component sensitivities, and all components of the stress tensor is presented along with a formulation for the recovery of displacement and stress components in the interior of the object under consideration. Discussion of computational issues related to the overall efficiency of these formulations is given, along with numerical results to demonstrate the accuracy and efficiency of this approach.

Kane, J. H.↗

High-resolution sunspot observations

A six-hour sequence of observations of the sunspot BB 1680, NOAA 5612 obtained with the 65-cm vacuum reflector on August 2, 1989, is presented. The inflow of penumbral material to the umbra was found to be limited to the inner half of the penumbra. The outer half of the penumbra shows the Evershed effect outward flow extending beyond the penumbra.

Zirin, H.↗

A high-speed distortionless predictive image-compression scheme

A high-speed distortionless predictive image-compression scheme that is based on differential pulse code modulation output modeling combined with efficient source-code design is introduced. Experimental results show that this scheme achieves compression that is very close to the difference entropy of the source.

Cheung, K.-M.↗

Overview of optimal trajectories for flight in a windshear

Optimal flight trajectories for the B-727, B-737, and B-747 aircraft in the presence of wind shear are studied. The takeoff problem and the abort landing problem are considered with reference to flight in a vertical plane. In the former, optimal trajectories are computed by minimizing the peak deviation of the absolute path inclination from a reference value; in the latter, optimal trajectories are computed by minimizing the peak value of the altitude drop. Numerical computations show that, for both the problems under consideration, the optimal trajectories of the three aircraft show the same qualitative behavior. Hence, it appears that the near-optimal guidance schemes developed for the B-727 can be extended to the other two aircraft, albeit with some quantitative modification.

Miele, A.↗

Optimal trajectories for the aeroassisted flight experiment. Part 4: Data, tables, and graphs

The determination of optimal trajectories for the aeroassisted flight experiment (AFE) is discussed. Data, tables, and graphs relative to the following transfers are presented: (IA) indirect ascent to a 178 NM perigee via a 197 NM apogee; and (DA) direct ascent to a 178 NM apogee. For both transfers, two cases are investigated: (1) the bank angle is continuously variable; and (2) the trajectory is divided into segments along which the bank angle is constant. For case (2), the following subcases are studied: two segments, three segments, four segments, and five segments; because the time duration of each segment is optimized, the above subcases involve four, six, eight, and ten parameters, respectively. Presented here are systematic data on a total of ten optimal trajectories (OT), five for Transfer IA and five for Transfer DA. For comparison purposes and only for Transfer IA, a five-segment reference trajectory RT is also considered.

Miele, A.↗

Project ARGO: The design and analysis of an all-propulsive and an aeroassisted version of a manned space transportation vehicle

The Senior Aerospace System Design class at the University of Michigan undertook the design of a manned space transportation vehicle (STV) that would transport payloads between low earth orbit (LEO) and geosynchronous earth orbit (GEO). Designated ARGO after the ship of the Greek adventurer Jason, two different versions of an STV that would be based, refueled, and serviced at the Space Station Freedom were designed and analyzed by the class. With the same 2-man/7-day nominal mission of transporting a 10,000-kg payload up to GEO and bringing a 5000-kg payload back to LEO, the two versions of ARGO differ in the manner in which the delta V is applied to insert the vehicle into LEO upon return from GEO. The all-propulsive ARGO (or CSTV for chemical STV) uses thrust from its LH2/LOX rocket engines to produce the delta V during all phases of its mission. While the aeroassisted ARGO (or ASTV for aeroassisted STV) also uses the same engines for the majority of the mission, the final delta V used to insert the ASTV into LEO is produced by skimming the Earth's atmosphere and using the drag on the vehicle to apply the required delta V. This procedure allows for large propellant, and thus cost, savings, but creates many design problems such as the high heating rates and decelerations experienced by a vehicle moving through the atmosphere at hypersonic velocities. The design class, consisting of 43 senior aerospace engineering students, was divided into one managerial and eight technical groups. The technical groups consisted of spacecraft configuration and integration, mission analysis, atmospheric flight, propulsion, power and communications, life support and human factors, logistics and support, and systems analysis. Two committees were set up with members from each group to create the scale models of the STV's and to produce the final report.

Wang, H.↗

Optimal penetration landing trajectories in the presence of wind shear

Aircraft penetration landing in the presence of strong-to-severe wind shear is investigated analytically. The optimal-control problem for vertical-plane trajectories is considered, using angle of attack as one control parameter with either (1) a power setting (PS) which remains constant at its preshear value, (2) a PS which increases to its maximum value, or (3) a PS which is controlled (as the second parameter). The problem formulation is explained in detail, and numerical results obtained with the primal sequential gradient-restoration algorithm of Miele and Wang (1986) are presented in extensive tables and graphs. It is found that the touchdown requirements can only be satisfied by optimal trajectories using scheme (1) (but only at low altitudes) or scheme (3); the characteristics of the latter trajectories are explored.

Miele, A.↗

Optimal penetration landing trajectories in the presence of windshear

The present consideration of optimal windshear-penetration flight trajectories in a vertical plane gives attention to the cases of either mere angle-of-attack control, with predetermined power setting, or both angle-of-attack and power setting controls. Inequality constraints are imposed on the angle-of-attack, the power setting, and their time derivatives. The performance index being minimized measures flight trajectory deviation from a nominal trajectory. Time is free, absolute path inclination at touchdown is specified, and touchdown velocity and distance are subject to upper and lower bounds. Three power settings are investigated.

Miele, A.↗

The velocity pattern of weak solar magnetic fields

The proper motion of magnetic elements on the quiet sun has been measured by means of local correlation tracking. The existence of a pattern in the intranetwork (IN) flow is confirmed. This velocity field is consistent with the direct Doppler measurement of the horizontal component of the supergranular velocity field. The IN elements generally move toward the network boundaries. By tracking test points, it is confirmed that the magnetic elements converge in areas corresponding to the magnetic network. But because the IN elements are of random polarity, they cannot contribute to the growth or maintenance of the magnetic network. By calculating the cross correlation between the magnetogram and Dopplergram, it is confirmed that the supergranule boundaries and the magnetic network are roughly correlated.

Wang, H.↗

The contrast of faculae near the solar limb

The contrast of solar faculae near the limb is measured on direct video images made with the 65 cm vacuum reflector at the Big Bear Solar Observatory. Six broad band filters with different wavelengths from red to violet are used. About 300 images were measured from observations made during the summers of 1983 and 1985. Over 20,000 faculae were measured. By averaging the contrast of faculae and plotting them vs heliocentric angle, it is found that contrast increases monotonically toward the limb for the shorter wavelengths; for longer wavelengths, contrast has a tendency to peak around mu = 0.15, and then decrease toward the extreme limb. The contrast increases as wavelength decreases.

Wang, H.↗

A study on the spectral models for waves in finite water depth

From an extension of the Wallops Spectrum (Huang et al., 1981) for the deep water waves, spectral models for waves in finite water depths are developed. Stokes wave expansions are found to offer a good approximation for intermediate water depth. The spectral function in this case is controlled by three parameters: the significant slope, the nondimensional depth, and the peak frequency. It is pointed out that solitary and cnoidal wave models must be used for the shallow water waves. The controlling parameters now reduce to the Urell number and the peak frequency. Even though the resulting spectral models place special emphasis on the energy-containing range of the spectrum, they are not limited to this range and they are not limited to any particular sea state. They are seen as offering a possible explanation of the variations in the special slope observed by previous investigators.

Huang, N. E.↗

Verification by remote sensing of an oil slick movement prediction model

The author has identified the following significant results. LANDSAT, aircraft, ships, and air-dropped current drogues were deployed to determine current circulation and to track oil slick movement on four different dates in Delaware Bay. The results were used to verify a predictive model for oil slicks given their size, location, tidal stage (current), weather (wind), and nature of crude. Both LANDSAT satellites provided valuable data on gross circulation patterns and convergent coastal fronts which by capturing oil slicks significantly influence their movement and dispersion.

Klemas, V.↗

Monitoring estuarine circulation and ocean waste dispersion using an integrated satellite-aircraft-drogue approach

The mounting economic pressure to extract oil and other resources from the Continental Shelf and to continue using the Shelf for waste disposal is creating a need for cost-effective synoptic means of determining currents in this area. An integrated satellite-aircraft-drogue approach has been developed which employs remotely tracked expendable drogues together with satellite and aircraft observations of waste plumes and tracers, such as dyes or suspended sediment. Tests conducted on the Continental Shelf and in Delaware Bay indicate that the system provides a cost-effective means of studying current circulation, oil slick movement, and ocean waste dispersion even under severe environmental conditions.

Klemas, V.↗

Monitoring estuarine circulation and ocean waste dispersion using an integrated satellite-aircraft-drogue approach

The author has identified the following significant results. An inexpensive, integrated drogue-aircraft-satellite approach was developed which is based on the Lagrangian technique and employs remotely tracked drogues and dyes together with satellite observation of natural tracers, such as suspended sediment. Results include current circulation studies in Delaware Bay in support of an oil slick movement model; investigations of the dispersion and movement of acid wastes dumped 40 miles off the Delaware coast; and coastal current circulation. In each case, the integrated drogue-aircraft-satellite approach compares favorably with other techniques on the basis of accuracy, cost effectiveness, and performance under severe weather conditions.

Klemas, V.↗

Verification by Remote Sensing of an Oil Slick Movement Prediction Model

The author has identified the following significant results. LANDSAT, aircraft, ships, and air-dropped current drogues were deployed to determine current circulation and to track oil slick movement on four different dates in Delaware Bay. Results were used to verify a predictive model for oil slick movement and dispersion. The model predicts the behavior of oil slicks given their size, location, tidal stage (current), weather (wind), and nature of crude. Both LANDSAT satellites provided valuable data on gross circulation patterns and convergent coastal fronts which by capturing oil slicks significantly influence their movement and dispersion.

Klemas, V.↗

Monitoring estuarine circulation and ocean waste dispersion using an integrated satellite-aircraft-drogue approach

The author has identified the following significant results. An integrated satellite-aircraft-drogue approach was developed which employs remotely tracked expendable drogues together with satellite and aircraft observations of oil slicks, waste plumes, and natural tracers, such as suspended sediment. Tests conducted on the Continental Shelf and in Delaware Bay indicate that the system provides a cost effective means of monitoring current circulation and verifying oil slick and ocean waste dispersion models even under severe environmental conditions.

Klemas, V.↗

A Cost-effective Satellite-aircraft-drogue Approach for Studying Estuarine Circulation and Shelf Waste Dispersion

The author has identified the following significant results. Satellites, such as ERTS-1, can be used to obtain a synoptic view of current circulation over large coastal areas. Since in turbid coastal regions suspended sediment acts as a natural tracer, cost is minimized by eliminating the need for expensive injections of large volumes of dye such as Rhodamine-B. One of the principal shortcomings of satellite imaging of coastal currents was its inability to determine current magnitude and to penetrate beyond the upper few meters of the water column. These objections were overcome by complementing satellite observations with drogues tracking currents at various selected depths. By combining the satellite's wide coverage with aircraft or shore stations capable of tracking expendable drogues, a cost effective, integrated system was devised for monitoring currents over large areas, various depths, and under severe environmental conditions.

Klemas, V.↗